A front mechanism having eight degrees of freedom has previously been disclosed. As shown in FIG. 4, in such a front mechanism, an upper rotating frame 102 is pivotally mounted on a lower traveling body 101 of a hydraulic excavator, and each member of this front mechanism, namely, a rear boom 103 extruded from the upper rotating frame 102, a front boom 104, a rear arm 105, a front arm 106 and a bucket 107 is connected to each other in this order with each foldable joint able to be folded freely up and down in each vertical swing, and furthermore the front boom 104 and rear arm 105 respectively have each joint rotatable around a front boom rotating axis 108 and a rear arm rotating axis 109 each supported longitudinally on the front boom 104 and front arm 106.
With such a front mechanism, work such as open channel side ditching, bank cutting, land cleaning and cutting in any arbitrary direction, and digging around a pole become possible.
Hitherto in controlling a front mechanism, multiple levers and pedals were installed in the cabin of the hydraulic excavator as manipulators corresponding one by one with each joint action. The manipulators were controlled in combination so as to generate the required working conditions.
However, in excavating works such as bank cutting, land clearing, side cutting and open channel side ditching, this traditional controlling method applying these multiple manipulators corresponding one by one with each joint action, has the following difficult problems. For example, in determining the position of the bucket for working, it is necessary for the axial direction of the rear arm to face vertically against the working surface without changing the position of the tip of the rear arm, and to direct the bucket to face toward the excavating direction. Usually these controls are very complex and it is inefficient to work in this way. Furthermore, in order to operate the bucket along the working side or toward a specified working direction, the operator must shift at least five manipulators in harmony, at one time, and this requires skill and experience and, even so, it is inefficient to do so.
Until now, owing to above mentioned cumbersome problems, it was difficult to put a power excavator having arms with multiple directions of freedom of movement, in practical use.